SOIyAR OBSERVATORY. l6l 



Various investigations not mentioned in the above summary are referred 

 to in other parts of this report. 



Of the events of the year, the completion of the proof that a magnetic 

 field exists in sun-spots, the remarkably successful performance of the 

 6o-inch reflector, and the evidence obtained with its aid of the selective 

 absorption of light in space call for special mention. Dr. Fath's observa- 

 tions of the spectra of nebulae and clusters, made last year at the Lick Ob- 

 servatory, indicate that no sharp dividing line can be drawn between the two 

 classes of objects. The Great Nebula in Andromeda gives a distinct solar 

 spectrum, and, as it is known to be enormously distant, it may possibly 

 consist of a countless swarm of solar stars, so closely crowded together 

 that they can not separately be distinguished with any telescope. Resolv- 

 able clusters, even of the open type, are very remote from the earth. The 

 demonstration by Professor Kapteyn and Mr. Babcock that the Andromeda 

 Nebula, as compared with a solar star, is about i magnitude brighter when 

 photographed through a red screen than when photographed without a 

 screen is of the greatest importance. Professor Kapteyn's previous in- 

 vestigation of about 1,400 stars seems to prove that violet light is more 

 absorbed than red light in its transmission through space. The absorption 

 coefficient is very small, however, and the impossibility of including faint 

 stars in the investigation made its quantitative determination extremely 

 difficult. The results obtained with the Andromeda Nebula and with three 

 star-clusters are of an entirely different order of magnitude. They even 

 suggest the possibility of using this method to measure the relative distances 

 of remote objects, whose parallax and proper motion are too small to be 

 detected. 



STAFF. 



Mr. W. S. Adams retained his position as superintendent of the computing 

 division until August i, and served as Acting Director during the absence of 

 the Director in Europe, in April, May, and June. He now has charge of 

 the newly-organized Department of Stellar Spectroscopy. Prof. F. H. 

 Seares, formerly Professor of Astronomy and Director of the Laws Ob- 

 servatory of the University of Missouri, was appointed superintendent of the 

 computing division on August i. Mr. Seares will also have editorial charge 

 of the Observatory publications, and will carry on researches in stellar pho- 

 tometry and other subjects. Dr. Arthur S. King has continued throughout 

 the year his work as superintendent of the physical laboratory. Mr. G. W. 

 Ritchey remained superintendent of construction until January i, when the 

 general duties of that position were assumed by the Director. Mr. Ritchey 

 has been given charge of the work of designing and constructing the loo-inch 

 Hooker telescope, and will also continue to direct the work of the optical shop. 

 Mr. Ferdinand EUerman has continued his work with the spectroheliographs 



